Dunno about foldable knives, but machetes and axes are ok as long as one can justify the presence of such tools. I carry them in my trucks all the time. One of the routes I travel has the occasional landslide which brings some earth and small trees onto the road. Once at a police roadblock, I was asked "Kenapa simpan parang dlm kereta?", I politely told the cop that it was in case of minor tree blockages dan aku tak nak berjanggut tunggu JKR datang potong pokok. The cop smiled and waved me on. A friend of mine who also travels the same route sarcastically told the cops at the roadblock, "Kalau takde parang, u mau I pakai gigi ke?". He related the incident to me about a week after his visit to the balai. The way we explain ourselves is rather important.